Abstract Number: PB0977
Meeting: ISTH 2021 Congress
Background: Platelet and coagulation activation are highly reciprocal processes. Activated platelets secrete several coagulation factors and expose phosphatidylserine. On the other hand, the coagulation cascade generates ligands for platelet receptors, such as thrombin and fibrin. However, the contribution of coagulation processes beyond thrombin and fibrin to platelet functions is an active area of research. Coagulation-related factors known to bind platelets include amongst others coagulation factor (F)XIIIa and activated protein C (APC), but their role in platelet functions is unclear.
Aims: To investigate thrombin-independent effects of coagulated plasma (factors) on platelet responses.
Methods: Modulating effects of hirudin-treated, coagulated (fibrin-depleted) plasma on platelets were evaluated via well plate-based aggregation and flow cytometry (PAC-1 binding and anti-P-selectin). Fura-2 loaded platelets were activated with CRP-XL concentrations that induced submaximal platelet activation, in combination with FXa, FXIIIa or APC, and changes in cytosolic [Ca2+]i were assessed. Spreading assays were performed on surfaces coated with FXIII(a), (A)PC, thrombin and collagen and were assessed by fluorescence microscopy.
Results: Platelets exposed to hirudin-treated coagulated plasma showed increased aggregation and surface activation markers, compared to resting plasma. Purified FXa, FXIIIa and APC each enhanced CRP-XL-induced rises in platelet cytosolic [Ca2+]i. Markedly, the potentiating effect of FXa was completely abolished by addition of different thrombin inhibitors. While FXIIIa and APC alone did not induce platelet activation in solution, coated FXIIIa or APC caused spreading. Interestingly, PAR-1 inhibition diminished spreading on APC, but not on FXIIIa. Our ongoing work is further exploring platelet receptors and their pathways involved in platelet spreading on FXIIIa.
Conclusions: Coagulated plasma promotes agonist-induced platelet activation. Measurements of calcium rises and spreading point to a role of FXIIIa and APC, but not of FXa herein, partly through thrombin-independent PAR-1 activation.
To cite this abstract in AMA style:De Simone I, Gibbins JM, ten Cate H, Heemskerk JW, Jones CI, van der Meijden PE. Coagulation and Anticoagulation Factors Affecting Platelet Responses Independently of Thrombin and Fibrin [abstract]. Res Pract Thromb Haemost. 2021; 5 (Suppl 2). https://abstracts.isth.org/abstract/coagulation-and-anticoagulation-factors-affecting-platelet-responses-independently-of-thrombin-and-fibrin/. Accessed November 29, 2021.
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